Inhibitor of the corrosion of a metal material such as steel

Abstract

The invention relates to a corrosion inhibitor for a metal material such as steel, of the type consisting of an aqueous solution containing an alkali metal nitrite, wherein said solution contains 0.01 to 0.3 mol/l of an alkali metal nitrite, 0.01 to 0.3 mol/l of an alkali metal phosphate, and phosphoric acid in a proportion of a quantity sufficient to maintain the pH of said solution, measured at ambient temperature, between 6.9 and 7.2.

We claim: 
     
       1. An inhibitor of the corrosion of a metal material consisting of an aqueous solution containing 0.01 to 0.3 mol/l of an alkali metal nitrite, 0.01 to 0.3 mol/l of an alkali metal phosphate and phosphoric acid in a proportion of a quantity sufficient to maintain the pH of said solution, measured at ambient temperature, between 6.9. and 7.2. 
     
     
       2. The corrosion inhibitor as claimed in claim 1, wherein the molar concentrations of alkali metal ions originating from the nitrite and of alkali metal ions originating from the phosphate do not differ by more than 15%. 
     
     
       3. The corrosion inhibitor as claimed in claim 1, wherein said solution also contains a wetting agent. 
     
     
       4. The corrosion inhibitor as claimed in claim 3, wherein said wetting agent is a nonionic or anionic wetting agent. 
     
     
       5. The corrosion inhibitor as claimed in claim 3, wherein said aqueous solution also contains a foam-suppressing agent. 
     
     
       6. The corrosion inhibitor as claimed in claim 1, wherein the total concentration of alkali metal ions from said nitrite and phosphate is greater than 0.10 mol/l. 
     
     
       7. The corrosion inhibitor as claimed in claim 1, wherein said metal material is sheet steel coated on one side with a layer of a zinc-nickel alloy, and said inhibitor is applied to the non-coated side of said sheet steel preventing the appearance of stains on said alloy when said sheet steel is coiled.